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Improving nutritional quality of cultivated blueberry by enhancing phenolic recovery

Introduction As main dietary antioxidants, phenolic compounds are considered important functional ingredients that can improve the nutritional quality of food. Post-harvest processing methods may affect content and stability of phenolics, therefore, the purpose of this study was to investigate the influence of different processing methods (pasteurization, freeze-drying, and high- intensity ultrasound) on blueberry phenolic compounds, antioxidant activity, and polyphenol oxidase (PPO) activity. Methods Cultivated blueberry (Vaccinium corymbosum L.) puree was pasteurized (80 °C/5 min), freeze- dried and treated with high- intensity ultrasound using different amplitudes (30, 45 and 60µm) and treatment times (3, 6 and 9 min). Total phenolic content (TPC), individual phenolics (by HPLC), antioxidant activity (by DPPH and FRAP) and PPO activity were determined prior to and following processing methods. Results TPC in freeze-dried blueberries was 33% higher, as compared to untreated puree. Pasteurization has caused significant reduction of TPC (p=0.041), in particular anthocyanins which content was reduced for almost 80%. Highest phenolic recovery was observed after shortest ultrasonic treatment at amplitudes 30 and 60 µm, although no significant changes were observed between ultrasonically treated samples, which was also confirmed with principal component analysis. Both DPPH (p=0.031) and FRAP (p<0.001) methods confirmed the highest antioxidant activity of the freeze-dried sample. Freeze- drying has also been shown to be the most effective method for inactivating PPO with remaining only 7% of enzyme residual activity. Discussion This study is a comparative report on the effect of traditional (pasteurization) and modern processing technologies (freeze-drying, high- intensity ultrasound) on cultivated blueberry phenolics and PPO activity. The results have shown that freeze-drying is an efficient method for preserving phenolic compounds and inactivation of PPO, that is highly desirable. High-intensity ultrasound treatments preserved the content of phenolic compounds while pasteurization had a deleterious effect. It can be concluded that modern processing technologies should be competitive alternatives to traditional food processing technologies.

phenolics ; antioxidants ; freeze-drying ; high-intensity ultrasound

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